The long term objective of this study is a better understanding of the interaction of genetic and environmental factors in the etiology of human neurological disorders through the study of the specific disorder, Tourette syndrome (TS). Understanding the genetics of TS will be helpful in clarifying the role of environmental factors and may elucidate its pathogenesis. There is considerable uncertainty over the genetics of TS and a large scale family study, with reasonably defined ascertainment and systematic diagnosis is needed to resolve the questions. We will collect data on 100-150 probands and their families. Detailed diagnostic interviews will be given to all probands and their first-degree relatives. Activities of whole blood COMT, plasma DBH, and platelet MAO will be measured on all these individuals. In selected high-density families (several affected members) more remote relatives will also be studied and all members will be typed for genetic markers for linkage analysis. These data will be used to test whether specific genetic models can explain the familial patterns observed and whether there is any evidence for etiological heterogeneity in the syndrome.